The present invention concerns vehicle wheels of any type and, in particular, a non-pneumatic tire designed to be capable of bearing a load without inflation pressure.
It is known that the reinforced rubber tire inflated to working pressure has come into common use, so great are its qualities of comfort and sturdiness. It has been successfully adapted to applications as different as passenger vehicles, construction equipment, airplanes, motorcycles, farm machinery, heavy trucks, etc. The inflation pressure makes it possible to bear a load and distribute it on the surface.
Although the reliability of a pneumatic tire has become remarkable, it is known that the risk of a flat is not totally eliminated. The problem is that, in case of loss of inflation pressure, or even more insidiously in case of a substantial reduction of inflation pressure, the tire is no longer able to render the service for which it is designed under good conditions. Hence, there has been a multitude of proposals for non-pneumatic tires (see, for example, U.S. Pat. No. 5,050,656), the object of which is to eliminate the main cause of tire failure (flats), but which have not come into use for lack of being able to offer a sufficient level of comfort and/or endurance and/or capacity to bear heavy loads. Hence, there have also been numerous proposals aimed at providing tires with a greater capacity to roll temporarily without inflation pressure, for example, as described in U.S. Pat. No. 5,535,800.
The proposal cited above has, however, the disadvantage that it is complicated, if not impossible, to design a tire whose sidewalls remain resilient and can tolerate suddenly mounting a curb without damage. In fact, the reinforcing elements incorporated in the sidewalls risk being bent, in case of very marked stress, to the point that their radially outer end joins their radially inner base. In that case, if those elements are locally gripped to the extent of resulting in very small radii of curvature, their breaking point or their elastic limit will be exceeded, depending on the materials used. The object proposed does not therefore provide sufficient safety, since there is a strong likelihood that the tire will be destroyed (or even worse, locally degraded in a dangerous but not immediately apparent manner) by certainly extreme but not abnormal stresses (shock on a sidewalk curb). An ordinary tire, even when greatly deflated, tolerates these stresses much better due to its very flexible sidewalls, incapable of bearing the load by themselves.
The state of the art shows, by wavering between radical solutions (non-pneumatic tire wheel) and the solutions providing tires with a limited capacity to roll without pressure, that the problem of possible tire failure is extremely difficult to solve.
Furthermore, even without tackling the problem of failure, a tire as currently designed presents other disadvantages to which we have become accustomed for a very long time. It can be observed that a bead is so designed that it can be mounted and demounted from the rim, while being able to transfer the working stresses between the tire and the rim through sufficient tightening of the tire on the rim. This requires a rather delicate adjustment. It results in the rather solid and rigid construction known. But considering service rendered the users, there is some waste of material, for the use of a portion of same can be explained only for securing the mountability and demountability of the tire.
It is also known that the compromise between comfort (all the greater the more flexible the sidewalls) and performance (precise steering, which results in stiffening the sidewalls and/or in developing smaller and smaller sizes for passenger vehicle tires) is very difficult to arrange. It is also known that there is a great propensity for tires of a passenger vehicle to lie down under the front wheel on the outside of a turn in case of high transversal acceleration. In this case, the tire works quite poorly, letting the tread go too much and bearing on the road with the shoulder of the tire.
The object of the present invention is to propose a non-pneumatic tire that can truly be used without inflation pressure, which will be capable, like the pneumatic tire, of bearing a substantial load while providing good comfort, good adherence and good capacity to transmit considerable lateral thrusts. It is a question of proposing an alternative solution to the pneumatic tire. It is not simply a question of providing a tire with the temporary capacity to run flat.
The invention proposes a resilient non-pneumatic tire having an axis of rotation and essentially containing a tread carried by a resilient bearing structure radially situated inside said tread and defining, at least partially, an inner cavity of revolution, said bearing structure comprising:
a zone of attachment radially on the side of the axis of rotation, for the locking of said bearing structure on means of connection to a hub, and said zone of attachment being axially placed between the lateral limits of said bearing structure, said attachment zone being designed for contacting said means of connection to a hub, said means of connection to a hub being designed to form a rigid assembly,
a plurality of support elements, extending essentially crosswise, placed between the zone of attachment and the tread, said support elements being juxtaposed circumferentially and distributed all around the circumference, the support elements being fitted in said zone of attachment, each support element containing a bundle of superposed resilient base pieces, separated by a layer of elastomer adhering to each of the base pieces, so as to form a beam capable of undergoing bending stress,
an interconnecting structure between the support elements, arranged so that a portion of a radial stress of a support element is transferred to the adjacent support elements circumferentially, while allowing differences in displacement between adjacent support elements.
The capacity to bear a load, in the proposed non-pneumatic tire, is due essentially to the support elements. Distributed circumferentially, the support elements successively come into play for contribution in taking up the load when the non-pneumatic tire is rolling. Several preferably come into play at the same time in the footprint. The support elements are transversely oriented and essentially stressed on bending in order to make their individual contribution to taking up the load (that is, the so-called xe2x80x9cZxe2x80x9d stresses). Other stresses do exist, but it will be apparent that the elements are essentially stressed on bending.
Turning to the embodiments of each support elements, it will be shown that they comprise a bundle of flexible base pieces each of which is ribbon-like. The flexible base pieces are stacked radially, with insertions of elastomer adhering on each of the flexible base pieces. The beam thereby built is able to sustain bending in a radial plane. This feature of the support elements is however by no means limitative, namely if it is noted that the support elements have to sustain other deformations, since they do not all deform in a identical way simultaneously, as it will become more apparent hereunder. By describing that the means of connection to a hub form a rigid assembly, it is intended to point out that the whole deflection between the ground and the axis of rotation comes from the deflection of the non pneumatic tire, and not from a rim, a wheel or any suitable device for connecting to a hub, just like a conventional pneumatic tire with respect to its wheel.